Optical communications systems utilize modulated light, i.e., optical signals, through light channels or fiber optic cables to transmit information between devices. For example, transmission of broadband signal content, such as analog multichannel video, may include the use of narrow line width light sources in conjunction with low loss, single mode optical fibers (SMF). In optical communication systems, a light beam is modulated in accordance with the information to be conveyed and transmitted along the optical fiber to a receiver.
Long distance transmissions in optical fiber or in the passive optical network where a power split is necessary, especially for CATV applications, may require high fiber launch power for better performance, such as, to achieve a required/desired signal to noise ratio. However, if the optical power input to a fiber in the optical communication system is too high, a phenomenon known as Stimulated Brillouin Scattering (SBS) may occur. With SBS, a portion of the light input to the fiber is reflected and the power level of the light transmitted through the fiber is reduced below the intended power level, among other deleterious effects. SBS can reduce the quality of the signal output from the fiber in the form of, such as, noise rise and thereby affect the performance of a communication system.
Fiber nonlinearities limit a maximum power that may be launched into an optical fiber. Fiber nonlinearities represent the fundamental limiting mechanisms to the amount of data that can be transmitted on a single optic fiber. For a single wavelength system, stimulated Brillouin scattering (SBS) puts a limit to the maximum launch power in many communication applications before the impact of other fiber nonlinearities become relevant.
A common scenario in which SBS occurs is when an optical beam of narrow optical spectrum is launched into an optical fiber with a power above a threshold power level. If the power within the SBS gain line width is kept below a SBS threshold power level, the SBS should remain adequately suppressed. Unfortunately, the SBS threshold power level is either too low for current applications or too low for evolving optical communications systems that would benefit from higher launch power in to the optical fiber. For instance, for standard single mode fiber (SMF) is typically in a range of only about 6-7 dBm (4-5 mW) depending on the fiber length. Prior attempts to increase the SBS threshold have resulted in some system degradations that continue to limit the launch power or may incur some additional costs or some limit in SBS suppression.
Thus, techniques are desirable for raising the SBS threshold, e.g., above 6-7 dBm (4-5 mW), so that launch power in to an optical fiber can be successfully increased is desirable in many applications.
It is noted that while the accompanying FIGS. serve to illustrate embodiments of concepts that include the claimed invention, and explain various principles and advantages of those embodiments, the concepts displayed are not necessary to understand the embodiments of the present invention, as the details depicted in the FIGS. would be readily apparent to those of ordinary skill in the art having the benefit of the description herein.